Control System for Electromagnetic Pumps

ABSTRACT

A control system for controlling electromagnetic pumps, such as electromagnetic driven membrane pumps, has at least one microprocessor and at least one sensor, the microprocessor controlling the power supply to at least one electromagnet whose changes in emitted magnetic field causes at least one moving part, directly or indirectly, to perform an oscillating pumping movement. The control system has at least one positioning sensor which senses the moving part&#39;s position in the electromagnetic driven pump. By use of the positioning sensor&#39;s measurements, the pump can be controlled with great accuracy. A method for controlling electromagnetic pumps is also provided.

TECHNICAL FIELD

The present invention concerns a control system for operatingelectromagnetic pumps. More specifically, the invention relates to acontrol system and method in accordance with the claims.

TECHNICAL BACKGROUND

Electromagnetic pumps that apply pressure or negative pressure are foundin a large variety of variations and sizes and are used in manydifferent applications, everything from large industrial pumps to verysmall pumps for medical purposes. The diverse areas of use forelectromagnetic pumps such as membrane pumps results in a plethora ofrequirements put upon the performance of such pumps. A significantproblem for buyers of membrane pumps is that the supply of pumps frommanufacturers is to a large degree standardized to just a few differentmodels, largely because pump manufacturers seek economies of scale intheir production. The limited diversity of pumps means that there existsa need for more efficient control systems. This would allowmanufacturers to satisfy specific user needs in a much better way andthereby reduce costs as well as improve the performance of products thatcontain a pump. Today there is a lack of good quality, simple,standardized, low maintenance and inexpensive control systems forelectromagnetic pumps.

It is quite common that membrane pumps are driven with the aid of one ormore electromagnets. An electromagnet produces a back and forth movementthat for example causes the membrane to produce a pumping movement. Anadvantage with electromagnetic driven membrane pumps is that they aremore closely coupled to the membrane which renders it possible forexample to vary the length of stroke, which can not be accomplished bymembrane pumps powered by rotating motors with an eccentric.Furthermore, electromagnetic pumps are comprised of very few detailswhich make them inexpensive to manufacture. Electromagnetic pumps arestill less common despite this because of several problems that resultin the fact that an electromagnet is not obviously better at powering amembrane pump compared with a rotating motor. A significant problem withelectromagnetic driven pumps is that they are difficult to gear up forhigher pressure without introducing lever that entail more details andadditional friction. Yet another problem is that it is difficult tooptimize electromagnetic pumps to turn precisely at their closingposition without hitting the bottom of the pump. Hitting the bottomresults in a shorter life span and turning to early results in poorerpressure performance. Electromagnetic pumps are therefore often pre-setto a certain pressure that can not be changed, which in turn is often aproblem because this results in significant limitations. Still anotherproblem with electromagnetic pumps is that they are more complicated tocontrol than pumps with a rotating motor and they often can only becontrolled by the amount of voltage.

Additional problems that exist originate from the actual implementationand use of pumps. During the use of oscillating pumps such aselectromagnetic pumps and pumps with rotating motors with eccentrics,oscillations are created in pressure and flow. These are in many casesunwanted and can for example disturb measuring sensors which measure thepumped medium. So called air capacitors, a large vessel or volume, areoften used to even out the flow in order to minimize the disruptingoscillation. This is not however always a good solution because theytake into use a lot of space and the pumped medium risks being mixed inthese vessels before the medium finally reaches the gas sensor. Thisreduces for example the sensitivity and the response time of themeasuring system. Another problem with the use of pumps is that flow isaffected by how high the pressure is in the system. It is often desiredthat flow and pressure be constant. The performance of the pump dependsa lot on if the surrounding pressure for some reason changes. This meansthat one must measure pressure or flow or both with good precision andin many applications this is necessary in order to control the pump.This increases the cost and complexity of the system. Yet anotherproblem is when several pumps must be coordinated in order to attain acommon result, such as the mixing of gases. This creates very complexsystems with several flow meters, pressure meters and valves. It is alsoa problem to acquire a control system that is completely free fromcalibration and that is not affected by operation and aging.

Because of the above mentioned problems systems and products thatinclude pumps often give rise to very intricate designs comprised ofmany details malting production very costly.

PRIOR ART

In the Swedish patent application SE7503408 optical sensors are used forsecuring that the pump does not reach its closing position by digitallyreading a logical one or logical zero in order to stop or start theelectromagnet, however this solution differs greatly from the solutiondescribed herein, because their solution lacks information on whathappens during all the remaining time that is comprised of the time themovable part is in all the other positions than just the two closingpositions that are read. Nor does it have an incremental disbandmentwhich is necessary for freely being able to vary the increments strokefor stroke during the time the pump pumps. It was suggested that a holewhich can be moved with the aid of a thread be used for variableincrements. Patent document U.S. Pat. No. 6,616,413 describes asensor-based control system that automatically adjusts the resonancefrequency of an electromagnetic pump through induction.

Even if existing electromagnetic driven membrane pumps many timesachieve there purposes, none of these combine the advantages from bothmembrane pumps driven by a rotating motor and membrane pumps driven byelectromagnets without any of the disadvantages entailed by both types.The purpose of the present invention is therefore to bring about amembrane pump which encompasses the advantages from the respective typesof membrane pumps essentially without any of there disadvantages. Thissystem differs greatly from the system described herein, because theirsystem lacks the precision and accuracy needed to solve all the problemsdescribed herein and essentially aims to optimizing efficiency.

All the earlier mentioned problems result in that there exists a greatpotential for improving control systems for electromagnetic pumps. Byutilizing the wide controllability and very direct coupling to the powersource of electromagnetic pumps, it is possible to solve all the aboveproblems in an eloquent manner and greatly improve and increase theareas of use for electromagnetic pumps, compared to pumps with arotating motor as well as currently existing electromagnetic pumps whichlack the control system described herein.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be described in detail in the following text withreference to the enclosed schematic drawing which shows, in anexemplifying purpose, the current preferred embodiment of the invention.

FIG. 1 shows a control system according to the first executed form ofthe present invention.

THE CONTROL SYSTEM

With reference to FIG. 1 a control system is shown according to thepresent invention. The system is driven by an electric power source thatprovides control voltage and supplies the system, via a voltage reader5, with the energy needed to drive the system. The system consists of atleast one microprocessor 1 that gathers all the data, stores the data,computes the data and sends the data onward. Data is gathered from atleast one position sensor. Preferably the control system also containsat least one temperature sensor 4, at least one electric current meter 9(ammeter) and at least one voltage measurer 8 (voltmeter). Inalternative embodiments additional variations of the sensors may beutilized. The gathered data from the sensors are computed by themicroprocessor and thereafter control signals are sent to an electriccircuit 7 which in turn controls the electromagnets power supply. Theelectromagnets affect in turn a moving part whose position and movementis detected by at least one position sensor that preferably consists ofat least one optical transmitter 2 that sends out light to at least oneoptical receiver 3. The control system also contains a network interface6 that allows for several pumps to be controlled and/or for theircooperation with each other.

The Membrane Pump

The control system is designed to control several different types ofelectromagnetic driven pumps. In the exemplifying design of FIG. 1 thecontrol system is used to control an electromagnetic driven membranepump. The example should not be seen as a limitation on patentprotection for a control system in accordance with the present inventionbecause the control system is essentially designed to be used for allelectromagnetic driven pumps. The membrane pump consists of a gable 22that also contains circular hose connections. The gable 22 is joinedtogether with a flange 20. In the space between the gable 22 and theflange 20 exist a schematic drawing of a clack valve (check valve,non-return valve, one-way valve or other device for preventing backflow)21 which can be comprised of for the purpose appropriate type of clackvalve. A membrane 18 is clamped between the flange 20 and an additionalflange 19. This provides for the formation of a pump chamber between themembrane and flange 20 with an intake and an outlet. An axle (the movingpart) 12 is connected (fastened) to the membrane. The axle is suspendedin slide bearings 14 and is designed to move in an axial direction. Theaxle has a wider part 17 that stretches out in radial direction. Thewider part 17 can attract either of the two circular electromagnets 15or 16 that surround the axle. The electromagnet attracts the axle'swider part 17 by the axle's wider part moving closer to theelectromagnet because of the magnetic field formed by the electromagnet.Through alternately activating the electromagnets 15 and 16 anoscillating pumping movement can be established in an axial direction.Alternatively, one of the electromagnets can be replaced by a spring.

The Positioning Function of the Control System

The axial movement of the moving part that is created by theelectromagnets' emitted magnetic field comes to different extent, atposition 13 on the axle (the moving part) to obstruct the light sentfrom the optical transmitter 2 to the optical receiver 3. The movingpart will in all positions to some extent always shade the light betweenthe optical receiver and the optical transmitter. The obstructed lightresults in a shadow whose size can be measured as analogous voltage atthe receiver. The analogous voltage results in that the positioningoptical sensor will have unlimited resolution. The optical receivermeasures all light within all the wavelengths it is sensitive to, thuslight can come from other directions and other sources and not just fromthe transmitter of the optical receiver. To remove these sources ofdisturbance, the optical transmitter is turned on and off with a veryhigh frequency intensity so that the system can often control how muchlight that actually comes from the optical transmitter. Suitably, anoptical transmitter and an optical receiver are chosen that togetherhave a light width (the width of the emitted or received cone of light)comprised of the distance between 10 to 11 that is larger than thepump's stroke length. A longer stroke length can however be measured bymaking a conic end on the axle (the moving part), but this howeverresults in higher precision requirements on the axle's suspension sothat no radial play occurs which the system might then misinterpret asan axial movement. The system has a temperature sensor 4 to compensatefor possible changes (temperature drifting) in the electromagnet and theoptical positioning sensor.

The Automatic Calibration of the Positioning Function

The system also includes a function for automatic calibration ofmeasurements to compensate for possible sources of error in the opticalmeasurement of the moving part's position. The source of errors in theoptical measurements could be caused by for example aging and wearduring the operation of the pump. The automatic calibration is achievedby a mechanically well defined zero position or by means of theelectromagnets mechanically setting the pump in its turning positionsand thereafter optically measuring and updating the information on wherethe turning positions are expressed with the optical system's indicationof position. The system is in this way protected from for example aging,operation or filth that with time could create differences in theanalogous values measured on the optical receiver. In this way the wholechain from the operation of the optical transmitter to the reception ofthe optical receiver is calibrated.

Control Voltage

The control system for the pump receives its power via a voltmeter 5. Bymeasuring the operational voltage the system is powered by, theoperational voltage's level also functions as control information forthe pump, and in this way it becomes compatible with pumps operated byregular electrical direct-current (DC) motors, which are the most commonexisting type of pumps on the market today. It is very advantageous toreplace different types of pumps with the controlled pump according topresent invention if the need arises to replace other pumps in existingequipment. A description on how this works will be described below.

The Pump (Control System) in Function

The pump (the control system) receives an external incoming voltage ofsix volts when connected to the voltmeter 5. The same voltage isparallelly connected to the microprocessor 1 at which it will turn on.The microprocessor begins by measuring the temperature of the system inorder to use the temperature to compensate for possible measurementerrors that originate from temperature. This takes place continuously inthe software and is not mentioned further in this description. Themicroprocessor causes the optical transmitter to flash with a frequencyof preferably 10 kHz. The microprocessor activates thereafterelectromagnet 15 with help from the operation of electromagnets 7.

The electromagnet pulls the pump's axle (moving part) in an axialdirection toward the electromagnet 15 until the moving part reaches itsturning position where it mechanically links with the electromagnet.Thereafter the microprocessor measures the voltage at the opticalreceiver 3. The voltage is both measured when the optical transmitter isturned on and off. The microprocessor calculates the differences involtage and stores it in the memory as a defined turning position forthe pump. The same procedure is executed for the other turning positionby first deactivating electromagnet 15 and instead activatingelectromagnet 16. The microprocessor now knows both end positions of thepump and can thereby avoid striking against the turning positions. Themicroprocessor will now continuously measure the size of the shadow tocontinuously control exactly where between the turning positions theaxle is found. With help from a so called linearity table the voltagedifferences can be translated to a specific position despite of that thesize of the shadow is not totally linear in relation to the voltagedifferences. Then the microprocessor measures the voltmeter 5 whichshows six volts. The microprocessor has for example earlier beenprogrammed that an incoming voltage of six volts gives a full strokelength and a stroke frequency of 6 Hz. The microprocessor has in thisexample been preprogrammed to recognize that the incoming voltage involts indicates the stroke frequency. The microprocessor then causes theaxle to oscillate by alternately activating the electromagnets back andforth. It uses the optical positioning sensor to change direction intime so that the pump avoids striking its end points which would causewear and tear. It will adjust the speed of the pump so that a frequencyof 6 Hz is achieved. The adjustment of speed can for example beregulated with higher voltage to the electromagnet. The method used inthis preferred solution, is that by using an essentially higherfrequency than the pump's speed, interrupt, turn off and on, the voltagecoming in as voltage control, six volts in this case, with the aid ofthe electrical circuit 7 that controls the power supply to theelectromagnet. It is therefore possible to minimize the number ofcomponents in the design and to avoid regulation of the voltage andtherefore it is also possible to avoid energy losses in form of voltagedrops in the control electronics 7.

If the operation voltage for the control system in this case is raisedto seven volts the system's control program will maintain the fullstroke length but raise the stroke frequency to seven Hz accordingly. Inthis way it is possible to imitate a direct-current (DC) motor and thushave the possibility to replace existing direct-current (DC) drivenpumps on the market. Changes in operation voltage can of course controlother things than frequency. Frequency can be held constant and thestroke length can be controlled by the operation voltage. Furthermorethe operation voltage can control the actual flow or pressure which willbe described later herein. A linear pump function can then be achieved.

The Network Interface

The operation voltage can also be kept constant and the pump can insteadbe controlled through the network interface 6 with the existingcommunication/network protocol that the pump has. The network interfaceis designed so that several control system can be controlled togetherand cooperate with each other and with other external sensors andsystems. This allows for pumps to be controlled together to cooperatewith each other, and also with other external sensors and systems.Through cooperation between several control system larger pumps can beoperated by several or larger electromagnets. By using the networkinterface several pumps can work in parallel with the aim that they cantogether produce a larger flow. Even connecting in series provides asatisfactory effect for improving pressure performance. Parallel coupledpumps can through the control system's network interface work timedelayed to compensate flow ripples through by letting the first pumppumps out when the second pump pumps in. More than two pumps even outthe ripples further. A further effect of network functionality is thatthe same bus can control several pumps with less electronics andconnections. The network interface can also be wireless.

Calculation of Pressure

The control system can also calculate from the pressure the pumpgenerates. Somewhat simplified the method for measuring pressure isdescribed according to the following. The size of the acceleration, inthe direction that the electromagnet pulls the moving part, is a measurein the difference in force between the force that the electromagnetproduces to pull the membrane and the counter-force that pulls themembrane in the opposite direction which stems from the positivepressure or negative pressure found in the pump chamber.

With the aid of the position sensor it is known where the moving partis, how fast it is moving and its acceleration at any given moment. Theforce that the electromagnet produces at every distance to the axel isalready known by way of measuring (calibration). When the accelerationis measured and compared with the known force the formula A=F1−F2 can beused to calculate the unknown force produced by the pressure in thepump. Later, when the force produced from the pressure is known it ispossible to calculate the pressure's size with the formula P=F/A.

Of course there are other factors which influence as for examplefriction in bearings, elasticity of the membrane, further elasticity,air resistance and temperature. However, the importance of theseparameters will depend on how every pump is constructed, and this is whythey are left out of this simplified description.

Apart from earlier mentioned areas of use, the control system can alsobe used to measure the pump's flow by way of flow performance/stroke atdifferent pressures is measured and stored in the pump duringproduction. Thus the flow can be calculated with the aid of the formula,Flow=Stroke frequency*Flow performance at the specific pressure.

Examples of Application for Pumps Equipped with the Control System

The control system is used to control the pump in conjunction withdosage. The pump can dose because the flow performance/stroke at everyspecific pressure is known from calibration during production. Thepumped volume=the number of strokes*flow performance/stroke at thespecific pressure.

The control system can also be used to control the pump during themixing of different mediums. With the aid of the control system thepump's flow measuring function together with the network function can beused to create a very simple and functional system that can with highprecision mix different mediums.

The control system can be used to gear up the pump. The pump can pump atfull stroke length and later, when it is needed, reduce the strokelength and oscillate close to the operating electromagnet. This willachieve a significantly larger force to operate the membrane at whichthe emitted pressure can gear up.

Even if the preferred embodiment of the control system and the methodfor controlling the control system have been described in detail herein,variations and smaller changes within the scope of the invention maybecome known for those skilled in the art and all such cases will beconsidered to fall within the scope of the following claims.

1-21. (canceled)
 22. Control system for controlling electromagnetic driven pumps as for example electromagnetic driven membrane pumps, including at least one microprocessor (1) and at least one sensor, where the microprocessor controls the energy feed to at least one electromagnet (15, 16) at which changes in the emitted magnetic field causes at least one moving part (12) to perform an oscillating movement to achieve a pumping effect and at which at least one position sensor is placed to sense the position of the moving part (12) in the electromagnetic driven pump, wherein the position sensor includes at least one optical transmitter (2) and at least one optical receiver (3), the moving part (12) of the pump shades the light between the transmitter and the receiver to an extent whose size depends on the moving part's position, and the microprocessor (1) is set to continuously calculate, in relation to the size of the shaded area, the moving part's position from the size of the shadow which corresponds to the voltage at the optical receiver (3).
 23. Control system according to claim 22, wherein the moving part in all positions shades the light between the transmitter and receiver.
 24. Control system according to claim 22, wherein the microprocessor (1), for automatic calibration of the position sensor function, is designed to record the voltage from the optical receiver (3) with the moving part pulled by the electromagnet (15, 16) to at least one known position.
 25. Control system according to claim 22, wherein the optical transmitter (2) is designed to flash with at least 20 times higher frequency than the stroke frequency of the pump.
 26. Control system according to claim 22, wherein sensors are set up to measure the pump's emitted pressure by measuring the moving part's (12) acceleration during the pump's stroke.
 27. Control system according to claim 22, wherein the microprocessor (1) is connected to at least one sensor (9) which is designed to record the current, that passes through the electromagnets (15, 16).
 28. Control system according to claim 22, wherein the microprocessor (1) is connected to at least one temperature sensor (4) to use measured temperature data for temperature compensation of the control system.
 29. Control system according to claim 22, wherein sensors are set up to measure flow with aid of known flow performance for each pump stroke at different pressures.
 30. Control system according to claim 22, wherein the microprocessor (1) is designed to be controlled by the incoming voltage level that is measured by a voltmeter (5).
 31. Control system according to claim 22, comprising a function where the pump is driven with constant frequency and flow is varied with the moving part's (12) stroke length.
 32. Control system according to claim 22, synchronized in time with external systems or sensors to control the pump to perform the pumping movement when it is most advantageous for the surrounding systems or sensors.
 33. Control system according to claim 22, comprising a function for control of the pump to produce single strokes of variable length.
 34. Control system according to claim 22, wherein the microprocessor (1) comprises a network function (6) rendering it possible to join together several control systems.
 35. Control system according to claim 33, designed to use flow measurement and the network function to control the pump during the mixing of gases.
 36. Control system according to claim 33, designed to utilize the network function to cooperate with several control systems to drive larger pumps by use of several or larger electromagnets.
 37. Control system according to claim 33, designed to use its network function to time delay the pump stroke between several connected pumps to even out flow ripples.
 38. Control system according to claim 33, designed to use its network function to control several parallel coupled pumps to increase flow performance.
 39. Control system according to claim 33, designed to use its network function to control serial coupling of pumps to increase pressure performance.
 40. Control system according to claim 22, designed to use flow measurement to control the pump with a linear function for flow proportional against the incoming voltage.
 41. Control system according to claim 22, designed to use pressure measurement to control the pump with a linear function for pressure proportional against the incoming voltage.
 42. Method for controlling electromagnetic driven pumps, as for example electromagnetic driven membrane pumps, with a control system according to claim 22, wherein the microprocessor (1) measures measurement values from at least one position sensor, which incrementally measures the moving part's position and movement, at which the microprocessor computes the measured measurements and adjusts the control of the energy feed to the electromagnet (15, 16) according to the desired performance of the pump.
 43. Control system according to claim 22, wherein the optical transmitter is configured to flash repetitively. 